NASA astronauts successfully installed a new ammonia pump on the International Space Station Monday during their third spacewalk to make the emergency repairs. The astronauts do not yet know whether their efforts were enough to restore the space station's cooling system to full capacity.

It took three spacewalks totaling more than 22 hours, but astronauts Doug Wheelock and Tracy Caldwell Dyson managed to move the 350-kilogram replacement pump into position. They tightened bolts and made connections so ammonia could flow into the module.

Flight Director Courtenay McMillan in Houston, Texas called the success "a big step in the right direction." She spoke to reporters after the astronauts completed Monday's seven hour 20 minute spacewalk - what NASA calls an extravehicular activity, or EVA.

"What we saw on the EVA, and what we saw from the pump during its check out that we did during the EVA, things look really good," said Courtenay McMillan. "So yeah, that was a huge relief for a whole lot of people."

The space station's cooling system has been running at half capacity for more than two weeks. On July 31, an ammonia pump failed after a spike in electrical current tripped a circuit breaker. Another module continued to pump coolant through a separate loop, but astronauts had to power down non-essential equipment to prevent overheating.

McMillan said the team should know soon whether the system is functioning properly again. If so, she said the space station operations will return to normal on Tuesday.

The space station's deputy program manager, Kirk Shireman, said the team did an outstanding job coping with what he called "a major malfunction."

"When you have half of the cooling down for the U.S. segment of the space station, you have not much room for error beyond that, not much margin," said Kirk Shireman. "Any additional failures could get really ugly for us. Yeah, from that perspective, we're very happy."

The three American crew members are spacewalkers Wheelock and Caldwell Dyson as well as Shannon Walker, who operated the station's robotic arm during the repair operation.

Shireman noted that back on Earth, hundreds of people have worked around the clock for the past two weeks thinking through the smallest details of the repair mission. The operation was made all the more difficult when the spacewalkers had to deal with a toxic ammonia leak during their first attempt to remove the faulty pump more than a week ago.

Shireman said that although the team is relieved after their successful spacewalk, NASA's concerns will not subside until the two cooling loops are functioning properly.

Flight Director McMillan said the crew members likely will take a break after their 16 days of dealing with the emergency repair operations. She said they would return to their research and science experiments later in the week.

Shireman noted that there are some research tasks that will have to be postponed due to time constraints because the astronauts had to focus on the repair mission. But he said he did not know of any specific scientific projects that would be curtailed.